The present invention relates to real-time communications systems and in particular to ethernet-based data networks. Real-time communications systems known from the prior art have the problem that standard ethernet participants cannot be integrated directly into the communications system, or standard ethernet participants cannot be coupled directly with a real-time communications system. The present invention is described in particular in the field of ethernet-based communications systems, for which a simple realization of a coupling unit is shown.
A real-time communications system essentially comprises many participants. In a special embodiment, which is typically employed in automation applications, the system has primary participants (so-called masters) and secondary participants (so-called slaves).
Within this real-time communications system, data are exchanged in the form of real-time telegrams. In these real-time telegrams, their precise position is decisive to enable putting together information correctly. Besides these real-time telegrams, there are also data exchange mechanisms that do not proceed in real time. These mechanisms are used for instance for startup and for display, for instance for diagnostic purposes, where time demands are low.
The term “real-time communication” is understood as communication in which the specified activities are performed virtually without any time lag, or in other words typically with a guaranteed maximum delay that is known beforehand to other systems.
In such communications systems, there is often a need to make access possible to the various participants of the communications system. For this purpose, PCs are generally used that have no direct coupling to the real-time communication. These PCs must be coupled to the system via coupling units. The coupling of PCs to the communications system is done for instance by means of network participants. It is also usual to couple PCs to the “ethernet (Office)”. The coupling function is performed by individual real-time communication participants.